Fuse plug



L. LUDWIG 2,080,667

FUSE PLUG May 18, 1937.

Filed April 8, 1956 INVENTOR. lac/.16 L udwl :3

-24 TTORNEYS.

Patented May 18, 1937 UNITED STATES PATENT OFFICE 2 Claims.

The invention relates to electric fuse plugs of the type having a fusible link contained in an interior recess. The main object of the invention is to provide means in such fuses which will extinguish the electric are formed when the fusible link is blown, so as to prevent the combustion of the link and the consequent formation of an excessive amount of gases. Another object is to provide simple means for liberating such gases as are formed without danger of rupturing any part of the fuse, and which when such gases are ignited will effectively extinguish the flames before they can reach the exterior of the fuse. A still further object is to construct the means in such a manner that they may be used with fuses of various types and construction, and added to such fuses without materially increasing their cost.

These and various other objects and advantages will be readily understood from the following description and from the accompanying drawing of preferred embodiment of the invention, in which, however, modifications might be made without departing from the scope of the appended claims. In the drawing:

Fig. 1 is a cross-sectional side view showing a fuse plug to which the invention has been applied;

Fig. 2 is a similar view showing a modification;

Fig. 3 is another, similar view showing still another modification;

Fig. 4 is another side view of a fuse plug showing how an arc is formed in the ordinary fuse as now constructed;

Fig. 5 is a side view of Fig. 1 shown with certain venting means added and with parts broken away; and

Fig. 6 is a top view of Fig. 5.

Reference is now made to the drawing in which the body member of a fuse plug is shown at Ill; the threaded metal shell, which forms one of the contacts, at H; the center contact which forms the other contact on the fuse at l2; the fusible link at I 3; the customary metal cap at H; and the transparent mica disc at l5.

While most modern fuse plugs are made with a weakened part [6 in the fuse link for the purpose of causing the fuse to burn out at this point, it is well known that on a short circuit with a heavy over-load an arc will form after the link is burned through and that this are will often continue between the two severed parts of the fusible link until practically all of the parts are burned away. Not infrequently the metal shell will even be melted at the point II where the fusible link is soldered to it. This is plainly illustrated in Fig. 4 where the arc is shown at A and the burned-away portion of the fusible link indicated by the dotted lines B. Not only may this cause the metal shell of the fuse to be welded to the metal shell of the fuse receptacle, but the excessive amount of gas created in the interior of the fuse will not infrequently rupture the mica disc or even blows off the metal cap. As these gases are often ignited, serious fires or other accidents may be caused to persons or property.

The object of this invention is to prevent the excessive burning of the fusible link and I accomplish this by the simple expedient of interposing a barrier l8, as shown in Figs. 1, 5 and 6. This barrier may be constructed in various ways. In Figs. 1, 5 and 6, it merely consists of a strip of flat insulating material, such as a piece of cardboard, which rests in the bottom of the interior of the fuse and at the top is provided with a v-shaped notch in which the weakened part of the fusible link is held. When the fuse blows" and an arc tends to form between the severed parts of the link, the arc is extinguished just as soon as the ends of the links are burned down so far that the arc is interrupted by the interposed barrier l8. Thus, only a very small portion of the link can be burned away. Furthermore, the barrier I8 is inserted under tension by being slightly bent, so that, when the link blows, the barrier will straighten out and its upper end be interposed in the arc between the ends of the link.

In Fig. 2 the barrier I9 consists of a strip of insulating material bent .in the shape of a V, the legs of which are held against the underside of the upper part of the fusible link. In Fig. 3 the barrier 20 is shown as constructed from a strip of insulating material which has been accordion-pleated. The barriers in the modifications are also inserted under tension.

In addition to preventing the excessive burning of the link and the consequent formation of an excessive amount of gas, I have also found it advantageous, in some cases, to provide spe- 'cial means in the fuse for liberating such gases as are created. These means are illustrated in Figs. 5 and 6 and consist in embossing a plurality of arcuated air passages 2| in the upper face of the metal cap l4 and to place a ring or washer 22, having similar arcuated air passages 23, underneath the mica disc [5.

With these means for venting the fuse, all danger of rupturing the fuse or causing fire by escaping ignited gases is completely removed. I am aware that fuses have previously been made with venting means to allow the escape of gases, but, except the passages through which the gases are caused to escape are correctly constructed, flames from the gases will often pass through such passages. This is impossible in the present invention. The curves of the air passages cause the gases to strike against one side of the passages as they flow underneath the washer 22. The gases must next pass around the outer edge of the mica washer and then out throughjthe air passage 2! in completely altered directions. This altering of the direction of the flow, causes the gases to be forciblyimpinged against the metal parts and effectively extinuishes the flames.

While I have shown and described a fuse plug in which the fusible link is brought right up in close proximity to the mica disc so that it may readily be shown when the fuse has blown, it will be understood that one or another of the barriers shown may be used with fusible links otherwise constructed, as long as the barrier is placed in such a manner in relation to the link thatit will be interposed between the legs of the linkas this is burned away. It will likewise be understood that while I have illustrated and described a fuse plug such as ordinarily made with a porcelainbody and a metal cap, the invention may as readily be applied to fuses of other construction such as for example, fuses made of glass. For this reason I do not intend to limit the invention to any particular make or construction of fuse, but intend to employ it in any fuse in which a barrier can be interposed between the legs of the fusible link or links employed.

Having described the invention and its objects, what I claim as new and wish to protect by Letters Patent is:

1. In a fuse plug of the type described, having an interior recess and a fusible link contained therein; a normally straight strip of resilient and non-conducting material; said strip inserted in the recess with one end resting in the bottom of the recess and the other end abutting against the inner side of the fusible link; and said strip held under tension, by being slightly arcuated, so that its upper end will be interposed in the are formed by the burning link, when the link blows, so as to extinguish the arc.

2. In a fuse plug of the type described, having an interior recess and a fuse plug contained therein and provided with a weakened part for causing the fuse to blow at that particular part; a normally straight strip of resilient and non-conducting material; said strip inserted in the recess with one end resting in the bottom of the recess and the other end abutting against the inner side of the fusible link and directly under the weakened part; and said strip held under tension by being slightly arcuated, so that its upper end will be interposed in the are formed by the burning link, when the link blows, so as to extinguish the arc.

LOUIS LUDWIG. 

